I have a meeting/vacation/trip to outer space planned. Will I need to be present, or can I catch up when I get back?

No, you don’t – once you receive access to the lessons, you'll have them forever, (as long as you are a valid member) which means that you can catch up, because you're never behind.

The way the class works is that you receive all the content at once, but always retain access to everything. This means that if your family, or life or job gets crazy for a while, the content will be waiting for you when you get back.

So no, you don't need to be present, and yes, you can absolutely catch up.